This invention relates generally to single-mode fiber couplers, and more particularly to single-mode fiber couplers wherein the coupling ratio is determined by the taper length and the diameter of the coupler structure in the fused coupling region.
A fused fiber optic coupler consists of two or more adjacent optical fibers, that are joined by heating to form a common region. Optical coupling is the phenomenon which transfers transmitted light from one fiber to another fiber in this common region. The amount of light transferred is determined by the length of the coupling region and the distance separating the cores of two fibers in this region. Light transfer is increased by increasing the coupling length and reducing the core separation distance. Low loss access biconical tapered couplers are described in U.S. Pat. No. 4,291,940 entitled "LOW-LOSS ACCESS COUPLER FOR MULTI-MODE OPTICAL FIBER DISTRIBUTION APPARATUS" wherein biconical taper sections of the fibers are fused together to provide optical coupling between the fibers. Also in U.S. Pat. No. 4,392,712 entitled "LIGHT DISTRIBUTOR" an optical coupler is provided with a plurality of optical fibers each having a tapered portion, and the tapered portion of the fibers are thermally fused together to form a light mixing section where the cores of the fibers are packed together in a single cladding.
These biconical type couplers are usually formed by fusing and stretching the fibers simultaneously.